Components made of titanium materials, especially titanium-based alloys, are of great significance in technical circles. Titanium materials display great strength while having a low density as well as good corrosion resistance and heat resistance. Particularly in the aviation and aerospace industries as well as in aircraft engine construction, components made of titanium materials are of great importance. However, at an elevated temperature in the presence of gases, titanium materials tend towards oxidation or sulfidation. Moreover, the resistance to wear and tear of titanium materials is limited due to friction, erosion and fretting. Besides, titanium materials have a tendency towards stress corrosion cracking.
In order to improve the behavior of components made of titanium materials, it is a known procedure according to the state of the art to apply a metallic coating onto the surface areas of components made of titanium materials. Such coating means that the area of application of components made of titanium materials can be expanded. In this context, components made of titanium materials are normally chemically or electrochemically coated or electroplated with nickel. It is likewise known from the state of the art to coat components made of titanium materials with platinum, chromium, zinc or copper.
When components made of titanium materials are electroplated, the problem is encountered that titanium materials passivate, which prevents proper adhesion of the metallic coating to a component made of a titanium material. As a result, upon exposure to air or water, a thin oxide film is quickly formed on components made of titanium materials, thus preventing proper adhesion of the metallic coating to the titanium component. Consequently, in order to electroplate a component made of titanium material, there is a need for a special pre-treatment of the titanium component for purposes of activating the surface of the component to be coated so as to remove the oxide layer or the passive layer and to prevent the renewed formation of the oxide layer.
For instance, European patent specification EP 0 072 986 B1 discloses a method for activating the surfaces of titanium components, in which method the surface of a titanium component is first wet-blasted with fine-grain aluminum-oxide particles, and the activation of the surface with a solution of chromic acid, hydrofluoric acid and hexafluorosilicic acid is carried out after the wet blasting. Chromic acid, however, contains hexavalent chromium (Cr6+), which poses a clear hazard to safety, the environment and health. Moreover, the abrasive wet blasting procedure cannot be carried out uniformly on components having complex geometries, so that a component to be coated cannot be activated uniformly on all areas of its surface.
Other methods known from the state of the art for the metallic coating of titanium components, for instance, with nickel, call for a heat treatment of the coated component in order to ensure proper adhesion of the metallic coating, as a result of which high costs are incurred. For an example of this, reference is hereby made to the state of the art in accordance with European patent specification EP 0 494 579 B1 and international patent application WO 90/03457 A1.